This invention relates to mechanical face seals, and more particularly to an improved mechanical face seal utilizing a double spiral groove configuration to minimize wear and leakage.
Mechanical face seals of the type referred to herein are particularly useful in high speed fluid operating devices, and generally include a pair of rings, a primary sealing ring and a mating ring which are formed with confronting, generally radial sealing faces which define an annular seal interface. One of the rings is fixed for rotation with a rotating shaft, while the other ring is non-rotatably secured to a housing in which the shaft is supported. Means are provided to normally bias one of the rings toward the other so that the seal rings normally engage under static conditions. Under dynamic conditions, pressurized fluid in the housing is caused by the geometry of the ring faces to move between the rings and overcome the biasing force and thereby to form a minute gap between the ring faces. Ideally, this gap is sufficient to prevent contact between the seal faces (to minimize heat and wear), and small enough to minimize fluid leakage across the seal faces.
The fluid under pressure in the housing is present adjacent one circumferential edge of the sealing ring interface, while the area adjacent the other circumferential edge of the ring interface is at a lower or ambient pressure. The edge exposed to the fluid under pressure could be at the inner diameter or outer diameter depending how the seal is arranged between the shaft and housing.
The confronting face of one of the rings is formed with spiral shaped pumping grooves which are inclined in a direction so that, when the shaft is rotated, fluid is pumped from the edge of the rings exposed to the fluid under pressure in between the sealing faces and toward the edge of the rings exposed to lower pressure. This fluid pumping action creates the intended gap between the rings which desirably is maintained over the entire range of the shaft speeds and pressures. Thus, there is little or no contact between the primary and mating ring faces under dynamic conditions.
It will be appreciated that it is important to control fluid "leakage," i.e., loss of fluid by passage fully through and between the sealing ring faces. To this end, it has been proposed to provide a double spiral groove pattern with reverse inclined pumping grooves in the seal face which, in effect, pump the fluid back toward the fluid under pressure within the housing. The intended effect is to utilize fluid present between the sealing faces of the seal rings to maintain the desired gap between these faces during shaft rotation while preventing loss of fluid or "leakage".